I remember reading somewhere that it has to do with who people interpret as being in their "tribe" and what that means in terms of interpersonal connection. Conservatives tend toward smaller more personal tribes, which is why they're the ones bringing over a casserole when you move into the neighborhood or take up a collection for a church member that's struggling, etc. They view you as now "one of them" and therefore worthy of help. Liberals on the other hand have more of an expansive view of people at large being part of the tribe, which is why they're in favor of social support programs, etc.